1. Field of the Invention
The present invention relates to a semiconductor device having a photoreceptor part that has an open part formed on a wiring structure layer layered on a semiconductor substrate, and a circuit part disposed adjacent to the photoreceptor part on the semiconductor substrate.
2. Description of the Related Art
Optical disks such as CD (Compact Disc) and DVD (Digital Versatile Disk) have recently come to account for a significant portion of information storage media. Through the use of an optical pickup mechanism in playback devices for these optical disks, a laser light is radiated along a track of the optical disk, and the reflected light is detected. The recorded data are retrieved based on variation of the reflected light intensity.
Since the data rate of reading from the optical disk is extremely high, the optical detector for detecting the reflected light is composed of a semiconductor element that uses a PIN photodiode having a high response speed. The faint photoelectric conversion signal generated in the photoreceptor part of the semiconductor element is amplified by an amplifier and outputted to a signal processing circuit of a subsequent stage. From the perspective of maintaining the frequency characteristics of the photoelectric conversion signal, and restricting the superposition of noise, the wiring length between the photoreceptor part and the amplifier is made as short as possible. From this perspective, and from the perspective of reducing the manufacturing cost of the optical detection device, the photoreceptor part, as well as the circuit part that includes the amplifier and other components, are preferably formed on the same semiconductor chip. Such an optical detection device is disclosed in Japanese Laid-open Patent Application No. 2001-60713.
FIG. 1 is a schematic plan view showing an optical detection device in which a photoreceptor part and a circuit part are disposed adjacent to each other on the same semiconductor substrate. The optical detection device 2 is formed on a semiconductor substrate composed of silicon. The optical detection device 2 has a photoreceptor part 4 and a circuit part 6. The photoreceptor part 4 includes four PIN photodiodes (PD) 8 arranged 2×2, for example. Light that is incident on the substrate surface from an optical system is divided into four segments and received. The circuit part 6 is disposed on the periphery of the photoreceptor part 4, for example. A CMOS 10 and other circuit elements, for example, are formed in the circuit part 6. An amplification circuit for the output signal from the photoreceptor part 4, as well as other signal processing circuits can be formed on the same semiconductor chip as the photoreceptor part 4 by using the circuit elements in the circuit part 6. Although not shown in FIG. 1, wiring connected to the circuit elements, as well as wiring connected to a diffusion layer that constitutes the photoreceptor part 4, are provided in the circuit part 6. These units of wiring are formed by patterning an Al layer that is layered on the semiconductor substrate.
FIG. 2 is a more detailed plan view showing the conventional photoreceptor part 4. In the silicon substrate in the photoreceptor part 4, electrons and holes are generated by the absorption of light, and the generated electrons are gathered as signal charges in a cathode of each reverse-bias PD 8. For example, An n+ region in which an n-type impurity is diffused at a high concentration is formed in the semiconductor substrate surface of each of the PDs 8 as a cathode region 20 of the PDs 8. For the anode region, for example, a separation region 22 composed of a p+ region in which a p-type impurity is diffused at a high concentration is formed in the peripheral semiconductor substrate surface of each cathode region 20.
The cathode regions 20 and the separation regions 22 are each connected via contact holes 24 formed in an insulation film on the semiconductor substrate surface by wiring formed, for example, by an aluminum (Al) layer or the like layered on the insulation film. The signal charges collected by each cathode region 20 are each read via wiring 26. The separation regions 22 is applied, for example, a ground potential by wiring 28.
FIG. 3 is a schematic sectional view showing the structure of the photoreceptor part 4 and the circuit part 6 in a cross section perpendicular to the semiconductor substrate along line A-A′ in FIG. 1. The line B-B′ shown in FIG. 2 corresponds to the line A-A′ in the photoreceptor part 4 shown in FIG. 1. This cross-section shows the structures of two of the PDs 8 of the photoreceptor part 4, and the CMOS 10 of the circuit part 6. A wiring structure layer 30, a protective film, or the like is formed on the semiconductor substrate on which the PDs 8, the CMOS 10, and other circuit elements are formed. The wiring structure layer 30 has a structure in which a plurality of Al layers for forming the wiring 26, 28 and the like, as well as a plurality of interlayer insulation films for insulating the Al layers from each other, are layered in alternating fashion. For example, in the wiring structure layer 30, a first interlayer insulation film 34, a first Al layer 36, a second interlayer insulation film 38, a second Al layer 40, a third interlayer insulation film 42, and a third Al layer 44 are layered in sequence on the semiconductor substrate 32. For example, the first Al layer 36 and the second Al layer 40 are patterned, and wiring 50, 52 and other wirings are formed in the circuit part 6. The third Al layer 44 constitutes a light-shielding film for shielding light to the circuit part 6. A TEOS (Tetra-EthOxy-Silane) film 54 and a silicon nitride film (SiN film) 56 are layered in sequence on the wiring structure layer 30.
The wiring 50 formed by the first Al layer 36 can be connected to the cathode region 20, the separation region 22, the source and drain of the CMOS 10, and other components via the contact holes 24 formed in the first interlayer insulation film 34 and other films under the wiring 50. The wiring 52 formed by the second Al layer 40 is connected to the underlying wiring 50 as needed via contact holes that are formed in the underlying second interlayer insulation film 38 and the like.
The wiring structure layer 30 and the overlying layers in the region that corresponds to the photoreceptor part 4 are etched back to increase the efficiency of light incidence on the PDs 8, and an open portion 58 is formed in the position of the photoreceptor part 4. Reducing the thickness of the wiring structure layer 30 in the photoreceptor part 4 by etching in this manner enhances the transmittance of light to the silicon substrate 32, and it is expected that the photoelectric conversion signal by reflected laser light will be obtained with a good intensity.
The interlayer insulation films are formed using materials such as SOG (Spin On Glass), BPSG (BoroPhosphoSilicate Glass), and TEOS (Tetra-EthOxy-Silane). These materials have moisture absorbing properties but are disadvantageous in that the absorbed moisture causes deterioration of the Al wiring and fluctuation of the element characteristics of the circuit part 6. In this regard, a silicon nitride film absorbs relatively little moisture, and the silicon nitride film 56 that is deposited over the interlayer insulation films on the circuit part 6 in the conventional technique functions as a moisture barrier film for the underlying interlayer insulation film.
However, in the conventional configuration, the interlayer insulation films are exposed on the inside of the open portion 58, and moisture can be absorbed from this exposure. Particularly since the side walls of the open portion 58 are adjacent to the circuit part 6, absorbed moisture from this portion easily causes the abovementioned wiring deterioration or fluctuation in the circuit element characteristics.
The reflected laser light or other light that is directed at the photoreceptor part 4 and is incident on the open portion 58 is suitably blocked by the light-shielding layer formed by the Al layer on the device surface, but the light can penetrate into the interlayer insulation film from the side walls of the open portion 56. The penetrated light can proceed into the inside of the circuit part 6 through multiple reflections at the Al layer, interfaces of layers having different refractive indices, and the like. Drawbacks occur in that such penetrated light enters transistors and other elements of the circuit part 6 and affects the operation thereof, and can generate noise in the electrical signals of the circuit part 6.